WIYN OPEN CLUSTER STUDY LII: WIDE-FIELD CCD PHOTOMETRY OF THE OLD OPEN CLUSTER NGC 6819

• Published in: The Astrophysical journal 2013-01, Vol.762 (1), p.1-13
• Main Authors: Yang, Soung-Chul, Sarajedini, Ata, Deliyannis, Constantine P, SARRAZINE, ANGELA R, Kim, Sang Chul, KYEONG, JAEMANN
• Format: Article
• Language: English
• Subjects: ASTRONOMY; ASTROPHYSICS; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CHARGE-COUPLED DEVICES; COLOR; DIAGRAMS; ELEMENT ABUNDANCE; Fittings; HYDROGEN; Imaging; INDEXES; IRON; LUMINOSITY; MASS; Open clusters; PHOTOMETRY; Segregations; STAR CLUSTERS; STARS; TELESCOPES
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/762/1/3

We present a comprehensive photometric study of the old open cluster, NGC 6819, using 1[degrees] x 1[degrees] field VI MOSAIC CCD imaging taken with the WIYN 0.9 m telescope. The resultant color-magnitude diagram (CMD) shows a well-developed main sequence (MS) extending from V ~ 14.5 mag down to our photometric limit of V ~ 21 mag. Fitting theoretical isochrones with the adopted values of the reddening and metallicity (E(B - V) = 0.14, [Fe/H] = +0.09 dex) to the observed CMD yields a distance modulus of (m - M) sub(0) = 11.93 + or - 0.10 and an age of ~2.6 Gyr for NGC 6819. Our wide-field imaging reveals that NGC 6819 is larger in areal extent (R = 13') than previously thought. The wide field also benefits our estimate of the degree of field star contamination, and ultimately yields improved measurements of the structural parameters (r sub(c) = 2'.80, r sub(t) = 38'.2, and r sub(h) = 7') and tidal mass of the cluster (M sub(tid) = 3542.4 M sub([middot in circle])). The flattened luminosity and mass functions indicate that NGC 6819 has experienced mass segregation as a result of its dynamical evolution. Our variability study of the cluster blue straggler star (BSS) population using the Welch-Stetson variability index (I sub(WS)) has revealed a number of variable BSS candidates.